id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
172	1dVar logq behaviour	Huw Lewis	Huw Lewis	"Email from Kjartan:


{{{
I remember you were talking about some testing of the two algorithms
you had performed.

I have generally been using the MINROPP minimiser but recently I 
tried running with LEVMARQ instead and saw quite a number of bad 
1D-Var solutions as a consequence.

Generally these solutions show a large (sometimes very large) spike 
in the specific humidity somewhere around the tropopause where my 
observation error description changes. The same files processed with 
the MINROPP minimiser show nothing out of the ordinary.

I am attaching an example [SEE ATTACHMENT TO THIS TICKET]:

ate* is the observation file with error description added
bgr* is the background with error description
ecmwf* is the background error correlation
cor* is the observation error correlation

I have also attached two plots marked LM and MR.

This file was by no means the only one. Using LEVMARQ is saw above 
20 solution profiles in a day being rejected because the humidity 
was above saturation as against only 2 using MINROPP. Also the O-B 
statistic clearly showed that something was going on in this region.

Looking at the LEVMARQ generated solution file above I am also 
somewhat mystified by the low value of J_scaled as it does not seem 
to me to be consistent with the very high values in the J_obs vector 
(also in the solution file).
}}}

This requires investigation and a fix!
"	defect	closed	normal	4.0	ropp_1dvar	3.0	fixed	logq